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James T Kirk

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About James T Kirk

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  1. The advice I gave above remains sound, Elanora reception issues post restack as a result of Mt Tamborine no longer being part of the SFN are mainly a result of auto tune functions and antennas needing repointing, thankfully it has quietened down considerably.
  2. Hello Elanora is well served by both Currumbin and Mt Tamborine transmitter sites. If your antenna is oriented vertically and pointing towards Currumbin, ensure you are using channels 34/571.5MHz, 35/578.5Mhz, 36/585.5MHz, 37/592.5MHz, 38/599.5MHz, 39/606.5MHz, 49/676.5MHz and 50/683.5MHz. (The Nine Network is on 35/578.5Mhz) If your antenna is oriented horizontally and pointing towards Mt Tamborine, ensure you are using channels 40/613.5MHz, 41/620.5Mhz, 42/627.5MHz, 44/641.5MHz, 45/648.5MHz, 46/655.5MHz, 47/662.5MHz and 48/669.5MHz. (The Nine Network is on 45/648.5Mhz) Another way of putting it: If you find you have an antenna pointing to Currumbin and the TV for the Nine Network is tuned to channel 45 on 648.5 MHz retune to channel 35 on 578.5 MHz. Conversely , if you find you have an antenna pointing to Tamborine and the TV for the Nine Network is tuned to channel 35 on 578.5 MHz retune to channel 45 on 648.5 MHz. If neither of the above apply, consider you may have an antenna/cabling issue to resolve, such things can appear channel specific. James
  3. AlanH I am quite happy to limit my communication to answering Liz, especially since the moderators want me to be nice. I have respectfully added my views to your responses above in red for clarity for the reader. James
  4. Hi Liz, In Australian capital cities the ERP of DAB+ and DVB-T are not always the same and also the patterns aren't all omni-directional, hence I would not advise assuming a direct correlation in ERP between DVB-T and DAB+ across the country. Hawkesbury Heights RF transmission is 300W in DQPSK, this is not an irrelevant emission and its influence would go well beyond 27km, easily double this primarily as a consequence of the modulation mode DQPSK used. In this situation we have 300W ERP line of sight working with terrain limited 50kW ERP. In essence Artarmon is launching 22dB greater power than Hawkesbury Heights and the signal levels at the receiver only need to be within 10dB of each other to have an influence on the receiver, that leaves the question of whether 12dB of terrain limitation from Artarmon is possible at Blacktown and of course this is highly likely based on the terrain profiler I ran before responding. The transmission mode used is all important since this determines the minimum carrier to noise ratio that is capable of delivering quasi error free reception and impacts the determination of the level required of reflections and/or alternate in band transmission sources before loss of reception. When a DAB+ receiver is impacted by two or more sources all but one is considered to be in band noise which reduces the receiver's ability to recover an error free signal, resulting in an unexpected reduced coverage area. On this basis if Hawkesbury Heights was turned off, it is entirely possible that your DAB+ reception would improve. Of course Hawkesbury Heights would not be turned off however your contacting the Commercial and National Broadcasters with some details of your reception issues could prompt an investigation that may instigate a revision of that sites antenna radiation pattern. If you were an experimenter, a vertically polarised directional antenna pointed to Hawkesbury Heights would verify that site is having an impact on you area by delivering stable reception. Re: "I'm imagining that the DAB transmission is kind of like a machine gun with the gap between bullets being the guard interval. This interval allows for the situation where if the bullet from gun A doesn't reach the receiver in good condition or at all then there is the opportunity for a bullet from gun B or C to be received instead a fraction later. I'm also assuming that each transmission site fires its bullets at precisely the same time perhaps coordinated by GPS timing?" I haven't heard an analogy for DAB+/DVB-T like that before and although I appreciate the creativity in reality the system does not provide second and third chances etc in the RF domain to recover the signal. I have attached a simple analogy used previously in training, it's not close to what really happens but will bring you closer to understanding than the machine gun. James
  5. Hello Liz Although you state you are a non technical person you are in fact much closer to the mark than those responding have chosen to acknowledge. "As a non technical person I would have thought a 50Kw 1.5Mhz wide channel would propagate differently to a 50Kw 7Mhz wide channel radiated from the same antenna not to mention I'd expect the error correction to be far more robust on the DAB signal when compared to DTV." You are so spot on, others noting the same 50kW ERP for both DTV and DAB is an utter irrelevance as compared to the error correction capability afforded DAB+ due the adopted modulation method as you correctly note. Responses such as this are inept and seriously flawed " 4 DAB+ channels fit into a TV channel. The total power of the channel is being measured so one would expect that the total power of the 1.5 MHz of the DAB+ channel would be 4 times higher than for a 1.5 MHz portion of a TV channel." This is an increase of 6 dB." Possible differences in horizontal radiation pattern ie antenna system gain and differences in licensed ERP leave no doubt this is a ridiculous statement to make. Going back to your "robust" comment, here's some technical stuff. What DAB+ does is use a different modulation scheme to DVB-T, DAB+ uses DQPSK whereas DVB-T presently uses 64QAM. (Slower data rate permits weaker signals to be recovered) In essence the difference between how much the received DVB-T signal needs to be above the noise floor over how much is needed for DAB+ is around 12dB, ie DAB+ can operate from a much weaker signal. All three DAB+ ensembles are being transmitted from Artarmon tonight and once you get to Blacktown, Artarmon reception is terrain dependent and the on channel repeater at Hawkesbury Heights becomes line of sight for you, again transmitting all three DAB+ ensembles. This may the issue you are facing, your DAB+ receivers with no directional antenna are struggling with multiple sources combined with terrain reflections. If your television at home from Artarmon is stable and reliable, this would tend to support this theory. Contacting the Commercial and National Broadcaster with some details of your reception issues could prompt an investigation. James
  6. You're welcome MLXXX On reading this post of 12 years ago, there's a few items in there that could be updated like changes to Seven and SBS, clarifications on constellations and more detail on timing in SFN's, but overall considering this was an off the cuff response to some woefully inaccurate posting by the originator, it's not bad. James
  7. Single Frequency Networks (SFN) in DTV Reception Problems Posted August 20, 2005 · Report post Digital Television and the SFN SFN A Single Frequency Network as applied to Digital Television Broadcasts in Australia is a technique that allows multiple transmitters with overlapping coverage to operate on the same channel. Steps are taken to minimise the risk of interference between transmitters in these overlapping areas by careful control of output power and timing. It is not a perfect solution and particular care needs to be taken by antenna installers to achieve a reliable service in these overlapping areas. Note on DVB-T In Australia, all DVB-T broadcast channels occupy 6.656250MHz of their 7 MHz bandwidth with a Coded Orthogonal Frequency Division Multiplex (COFDM) signal comprising 6817 carriers spaced at 976.563Hz apart. Most of these 6817 carriers are quadrature amplitude modulated (QAM) and every carrier is capable of carrying different information. A few carriers are fixed to a known amplitude and phase for the purposes of synchronisation and referencing and the majority carry the sound ,vision and text etc i.e. the payload is 6048 carriers. Generating and modulating each of these 6817 carriers individually was unthinkable until recent times. Now a process called Inverse Fast Fourier Transformation (IFFT) allows all 6817 carriers to be generated at once in a manner that spaces them specifically to minimise interference between each carrier (the coded orthogonal part of the process). The 7MHz system as used here with error correction capabilities versus desired payload allows for data rates around 19 Mbit/s (Seven and SBS) and 23 Mbit/s (ABC, Nine and Ten). Unfortunately we cannot insert pictures on this forum so I’ll try to describe a constellation pattern and how we can use it to observe if the QAM signal is working well or not and how received noise affects this display. The version of QAM used here is 64QAM, this means for the 6048 payload carriers there is 8 discrete phase changes of a carrier and 8 discrete levels of amplitude change, from this we have 64 combinations of amplitude and phase. If you imagine an 8 by 8 matrix of squares on a page and place a small dot in the centre of each of the 64 squares this would represent an excellent received signal. Keep in mind that a small dot here means the target is being hit in the same spot time after time after time. The position of the dots away from the centre of each target gives the operator of the transmitter information on the health of the transmitter. For those at the other end receiving the signal, the dots should be always found to be in the centre of the target. Now if these small dots represent a target being hit at the same point continuously and noise is introduced, the dots being fired at the target are shifted and what was a defined small spot grows larger with increasing noise and its edges become fuzzy. Eventually the whole 8 by 8 matrix becomes a blur, but the system keeps going. All is still well so long as it still lands somewhere in its own target. Should it hit an adjacent target or worse, an error is registered and then the bit error ratio (before viterbi) starts to worsen. If things continue to deteriorate the programme is lost very quickly. If you have noticed that you get sound blips or picture freezing occasionally when the fridge or dishwasher etc starts, then you probably have a marginal signal in your area, a poor installation, you’re in a mush zone or a bit of all. However I only seek to mention it here because it also indicates a noteworthy characteristic of DVB-T and that is as the received signal becomes weaker, reception becomes more susceptible to impulse noise. This is because the data in the payload carriers is amplitude and phase modulated (QAM) and any amplitude modulated signal can be affected. Anyone who has listened to AM radio has heard interference from car ignition systems, kitchen appliances and lightning etc. These common place interferers that cause noise on AM radio, may cause horizontal interference lines on analogue television and corrupted data in DVB-T causing intermittent freezing and audio blips or complete loss because the targets in the constellation as describe above have been missed. Simultaneous amplitude and phase modulation has been around and in use by us all for a long time. Some recent examples are Stereo AM radio and colour television. When AM radio became AM stereo, phase modulation had been used to allow left-right information to be transmitted and in 1975 when colour television started the colour sub-carrier was added and its amplitude and phase determined the colour and its intensity. Despite its vulnerability to impulse noise, the extremely complex error correction techniques manage in the majority of cases to cope with such impulse noise issues. It will not fix everything though, the receiver can’t recover the data if the signal is too low compared with the impulse noise. One of the nice things about digital television is that there is no ghosting of the picture, in fact ghosting isn’t possible. The receiver is able to disregard, up to a point, reflected signals from other sources such as buildings, water towers and hills. Built into the transmitted signal is a guard interval, 1/8 for (Seven and SBS) and 1/16 (ABC, Nine and Ten). This allows for reception of the main signal and echoes successfully so long as the echo delay does not exceed 128uS for (Seven and SBS) and 64uS (ABC, Nine and Ten). This level of tolerance to reflected signals or echoes allows the digital signal to be successfully received whereas the analogue could be rendered unwatchable. Furthermore it is this tolerance to echoes that allows the possibility of a SFN. The SFN As any good television antenna installer knows, the choice of receive antenna is only a portion of making a reliable service for the consumer. Cable lengths, the location of the antenna and its height on the home is all-important and makes a substantial difference to the result. The reason for taking such care is the surrounding topography and buildings can play havoc with predicted received signal levels. The very same topography issues are considered when decisions are made for locations of television transmitters. Once the transmitter location is decided upon, it will be a compromise, designed to get the best coverage to most of the people, however some will miss out. In the past with analogue television, smaller translators (transmitters that receive the main transmitted signal and retransmit it on another channel) were used to help cover those who missed out. You can do the same with digital television however there is not enough spare channels available while analogue is still to air. The solution was to have them all on the same frequency. As mentioned above, digital television receivers can cope well with echoes, so if you can time a second and third transmitter’s output so it appears as an echo within the guard band of that channel at the receiver, it will be treated as an echo and stable pictures and sound are produced. To support this, all transmitters in the SFN are fed with the same programme at around the same time, usually delivered by microwave link or optical fibre. There is timing information contained within the data stream and while the main transmitter is not delayed, the others are delayed to ensure their signals fall within the guard band of the main transmitter in its area influence. All are referenced to the GPS system to ensure each transmitter is on frequency and data rate is correct. Where does it go wrong (Mush Zones) Whether the topography is flat or mountainous there are areas where it all goes wrong. There will be areas where more than one transmitter within the SFN is received and their timing will be outside the guard band. By design these are preferred to be placed over water or in unpopulated areas as the topography permits. There will also be areas where they do fit within the guard band but are of similar levels and the receiver struggles to cope with deciding which is the main signal and which is the echo. These can be very difficult to sort. If you are installing an antenna in these areas, suddenly, rather than just knowing the gain and front to back ratio of a receive antenna, you also need to know the shape of its pattern and if it has any considerable acceptance on side lobes. The reason here is this antenna needs to be able to discriminate between the two or three signals ahead of the receiver thereby providing the receiver a signal it can cope with. In such difficult locations, knowing from what directions signals need to be avoided becomes as important as knowing the direction of the one you need. I hope this goes some way in helping to understand an DVB-T system operating as an SFN James
  8. Some responses “You are the poster who recommended viewers watch a signal from 70 km away using an expensive antenna system, when there is a translator within 8 km which is recommended by the antenna manufacturers and the Department of Communications requiring an inexpensive antenna.” Yes absolutely, dear reader, what is conveniently omitted is the person wanted to use VHF, was shaded from the local transmitter and was located on a bearing of minimum ERP from the local site, in other words VHF from Brisbane was superior. “Where do I get the info from? Not my vacuous head.” It is not for me state whether the poster’s head is vacuous or not, but genuinely, I see no reason to debate his suggestion. “I research the details of my post. In this case all transmitters must have licences and they are publically listed.” Google is certainly your friend. “As for power consumption for AM you have to know how the technology works, by passing exams which you have never done.” I think this may be your TVOCP/BOCP reference again. With all due respect to those who attained this, there are many who only stood in from of a transmitter during the TVOCP/BOCP exam and have never since, there are others who made it their career and have excelled. I will leave it to the reader to consider which category the poster fits best. “Other hallmarks of your posts include your lack of knowledge of Single Frequency Networks and DAB+ repeaters. That thread had to be shut down because of abusive posts which did not come from me.” This possibly was the pinnacle of the poster’s display of ineptness and belligerence, I would welcome anyone interested in SFN’s to read my posts of a decade or so ago. All, “Just to give you some of the economics, ABC local radio has 85 AM transmitters radiating 869 kW when there is no program which increases as the volume increases. The audio is carried in a pair of sidebands which require power of their own. At full volume the carrier is still 60 % of the radiated power and carries no audio. ABC Radio National 23 AM transmitters radiating 270 kW ABC NewsRadio 5 AM transmitters radiating 17 kW SBS 5 AM transmitters radiating 18 kW The transmitter electricity consumption is substantially greater than that because not only does the audio power have to be added also does cooling. DRM transmitters use between 50 - 60 % less power because they don't have a useless high powered carrier just a few low powered pilot tones for the same receiver functions. ABC Local Radio 161 FM transmitters radiating 3.005 MW effective radiating power + 132 FM transmitters totalling 10 kW of community funded retransmitters ABC Radio National 234 FM transmitters radiating 3.018 MW + 80 FM retransmitters totalling 6 kW ABC News Radio 76 FM transmitters radiating 2.97 MW + 2 retransmitters totalling 171 W ABC FM 68 transmitters radiating 5.084 MW + 30 retransmitters totalling 2.7 kW JJJ 58 FM transmitters radiating 5.067 MW + 181 retransmitters totalling 21 kW SBS FM 9 transmitters radiating 680 kW +137 retransmitters totalling 20 kW By comparison currently there is only 250 kW effective radiating power transmissions from 7 transmitters for the ABC/SBS permanently broadcasting. The electricity consumption of FM and DAB+ transmitters cannot be calculated from publically available data. None of the above statistics include standby transmitters AM local radio 40 transmitters 726 kW AM Radio National 10 x 214 kW AM Newsradio 4 X 32 kW” I will credit the poster with having far more time to put into this forum than I have, however the simplistic and ill-informed conclusions as described above are quite telling. Comparing DAB+ to AM radio is simply ridiculous. DAB+ transmitters with their multiple audio streams are 16% efficient in terms of power consumed to RF out and have a reliable coverage radius under 40km, the local ABC radio AM transmitters are 75% efficient when related to licenced transmitter power and reliably cover 200km radius. “By far the cheapest way of giving the 40 % of Australia living outside of the DAB+ areas digital radio is a very high powered DRM HF transmitter for Radio National/NewsRadio, and another for NT Local radio co-sited at the geographic centre of Australia, South of Alice Springs. Then every Australian will have at least 3 programs to listen to including whilst mobile in cars and boats. Local radio is still supposed to be "local" and DRM+ would work better in regional areas for coverage than the higher frequency DAB+ broadcasts. In addition DRM+ could easily carry the AM and FM programs of a commercial station along with advertising using pictures.” No question it is the cheapest but when the ACMA received the poster’s submission on this it was quickly filed away with the posters other wild submissions. I think this drawer is opened when the ACMA staff feel sad and need a good laugh. “Australia was at the forefront of digital radio and now has dropped the ball, we need DRM for our vast areas of low population density which is not the case in Europe and parts of Asia” We were never at the forefront, all that happened was some limited trials in the 90’s. DRM+ will be part of the digitisation solution for radio in this country, but it will never be implemented in the manner described by the poster. My question to the poster was "What AM and FM stations do you think have back ups" , the absence of a response indicates the poster does not know. I simply questioned the accuracy because I know the posters numbers were wrong. James
  9. I asked the question above simply because the information given by the poster is again inaccurate
  10. How do you come up with this stuff. What AM and FM stations do you think have back ups. James
  11. Hi Colin Genuinely I understand however I would not be too concerned about your "hacks" the HRP's for these sites on the Springfield bearing. Although they certainly are not omni-directional, in the direction of Springfield are: Bouddi (V) is -3dB ERPmax (640W) Rumbalara (H) is on ERPmax (300W) Forresters (V) is -8dB ERPmax (200W) James
  12. Hi Colin Yes indeed. One of the things we use is coverage overlap map showing the combination of the three local transmitters plus Sydney. It clearly shows residences in the same street can have field strength differences more than 24dB, Waratah St being a fine example, I think your attachments will certainly help Adrian sort his options. James
  13. Hello CMatten I don't know where Adrian is however when I checked the path profile from a central Springfield location to the three local transmitters and Sydney they are all woefully terrain obstructed. Adrian really has a challenge. James
  14. Dear Reader For the purposes of phase matching at UHF television frequencies, you can trust that two equal lengths of RG-6 will have the same delay. This is not some ideal world goal that the poster above is suggesting, just proven practical advice. James
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